The present disclosure relates to a bolt sensor, in particular, to a bolt sensor configured to optically indicate a fastened state of a bolt.
Civil engineering structures, such as bridges and tunnels, include many bolt-joint parts. The bolt-joint parts regularly undergo inspection for checking the presence of loose bolts. The inspection is typically performed by an inspector checking bolt-joint parts visually and/or by hammering.
Japanese Patent Application Laid-open No. 2002-4798 discloses a detection system in which a transponder including a strain sensor and a circuit for display and transmission are provided in a spacer to be installed between a nut and a body to which the bolt is applied. In this detection system, when the strain is generated in the system in the axial direction of the bolt, an LED of the circuit for display and transmission is lit. Japanese Patent Application Laid-open No. H11-118637 discloses a sensor bolt in which a sensor is embedded in a bolt and a display such as an LED is disposed in the head of the bolt. When the sensor bolt comes loose, the LED of this sensor bolt is lit.